1. Field of the Invention
The present invention relates to a portable display apparatus capable of performing real-time display of data fed thereto and a display control method. The portable display apparatus and display control method are advantageously applicable to, e.g., a digital still camera operable in a so-called movie mode.
2. Description of the Background Art
A display apparatus displays data fed thereto on its screen in the form of pixels represented by a group of image points or dots. Increasing the number of dots constituting the screen is successful to enhance image quality while reducing the pitch of dots is successful to enhance resolution, as well known in the art. A single still picture is generated by the dots or pixels. On the other hand, a movie is displayed in the form of a plurality of pictures, which are based on a display standard within a preselected period of time. Display satisfying the display standard is referred to as real-time display processing.
Sophisticated control for the real-time processing has customarily been executed by use of various kinds of devices including high-speed memories. However, such devices in general are difficult to obtain. This, coupled with the fact that access must be repeatedly made to memories for the management of data stored in the memories and for the input and output of data from the memories (e.g. double access), limits the real-time display capability available with the above control.
In light of the above, Japanese Patent Laid-Open Publication No. 124073/1994 proposes a system using low-speed memories for the continuous reproduction of a high quality movie. Also, Japanese Patent Laid-Open Publication No. 215120/1994 teaches a system for solving the double access problem and achieving high performance at low cost. These systems, however, belong to a family of asynchronous movie systems not satisfying the real-time display requirement. The systems taught in the above documents each write data in one of two memories field by field or frame by fame frame while reading data out of the other memory. This kind of procedure once writes data in each memory and therefore delays the display.
A synchronous system, as distinguished from the asynchronous system, directly outputs input data by synchronizing them to a vertical rate necessary for picture display. This system is applied to picture display based on, e.g., a VGA (Video Graphics Array) standard.
A digital still camera or similar miniature portable apparatus extensively used today is often powered by a battery in order to enhance portability. In a still picture mode, a digital still camera or similar image pickup apparatus does not record or reproduce data constantly in or out of a recording medium and has therefore little influence on the life of a battery loaded thereon. It is a common practice with the display apparatus to allow the user to see a scene being picked up on a monitor for rendering the display apparatus convenient to use. In this case, much of power available with the battery is consumed by the reading of signals out of a CCD (Charge Coupled Device) image sensor and the display of the scene on the monitor.
In the power saving aspect, the asynchronous system needs two memories each having a capacity greater than one frame and therefore consumes much power. This kind of system is not feasible for portable apparatuses.
As for the synchronous system capable of saving power, assume that color filters are implemented by a Bayer arrangement by way of example. Then, when signals are sequentially read out of the CCD image sensor, only two signals representative of pixels R (red) and G (green) and only two signals representative of pixels B (blue) and G are available with a first field and a second field, respectively. The prerequisite with color reproduction using the synchronous system is that the three colors R, G and B be output at the same time, so that the synchronous system cannot be simply applied to color reproduction. The synchronous system cannot implement a movie without resorting to memories, which aggravate power consumption.
In recent years, despite the trend toward the miniaturization and power saving of an apparatus, the number of pixels is ever increasing to meet the demand for higher image quality. The increase in the number of pixels will make it impossible to read signals out of pixels picked up within a period of time based on future display standards.
It is therefore an object of the present invention to provide a display apparatus with a real-time display capability and capable of effecting high quality display while saving power, and a display control method.
In accordance with the present invention, a portable display apparatus for displaying, based on a preselected standard, color data output from an image pickup device having pixels arranged in accordance with color filters respectively assigned to three primary colors R, G and B includes a mode selector for selecting either one of a still picture mode for displaying a single high quality picture by using the color data output from the pixels of the image pickup device and a movie mode for displaying a plurality of pictures by using the color data. A first synchronizing and interpolating circuit adjusts, in the movie mode, a timing in such a relation that the color data fed from the image pickup device and color data to be output are synchronized by an integral multiple, and interpolates void pixels intervening between the pixels of the color data fed to thereby generate a plurality of lines. A memory has a capacity greater than a single frame and temporarily stores, in the still picture mode, the color data fed from the image pickup device. A color data interpolating circuit interpolates the color data output from the memory. The color data output from the first synchronizing and interpolating circuit or the color data interpolating circuit are fed to a display while being synchronized also to a vertical timing different from the relation for synchronization.
Also, in accordance with the present invention, a digital still camera includes the above display device. The camera further includes a recording circuit for recording the output of the first synchronizing and interpolating circuit or the color data interpolating circuit in a recording medium. A reproducing circuit reads data out of the recording medium. The camera displays the output of the first synchronizing and interpolating circuit, the color data interpolating circuit or the reproducing circuit while synchronizing the output to a vertical timing different from a horizontal timing which implements the previously mentioned relation.